This invention relates to improvements in relief valves and more specifically to improving the adjustability of relief valves utilized in refrigeration systems while maintaining intact the sealing or seating engagement between the respective valve member and valve seat in the valve. Relief valves and especially those used in refrigeration systems are susceptible to special problems because of the cold or hot temperatures in which the relief valve may operate, depending on where in the refrigeration system this valve is positioned. Also, the use of modern synthetic materials, including a fluorocarbon resin commonly known under the trademark "Teflon" has become widespread at the sealing engagement of the valve because of its low coefficient of friction and good wear characteristics. An example of a relief valve including a fluorocarbon resin seal may be found in U.S. Pat. No. 3,425,444 issued Feb. 4, 1969 to the assignee of the present application.
Unlike synthetic rubber, used for seals in many relief valves for refrigeration service, Teflon is not a resilient material, and under relatively low compressive stress will not readily form a pressure-type seal against the valve seat. Although not resilient, Teflon will cold flow and when under compressive stress over a period, will eventually form a pressure-type seal.
Since individual relief valves may have differing characteristics, means are provided for setting or adjusting the initial leak pressure of the relief valve. Such adjustment means have included a threaded gland member which abuts one end of a spring biasing the valve member containing the Teflon seal against a stationary valve seat in the valve body. By turning the threaded gland member, the spring is compressed or allowed to expand in order to adjust the force on the sealing engagement, i.e., the initial leak pressure, of the valve. Since the Teflon sealing member has a low coefficient of friction against its valve seat, frequently, while turning the adjustment gland, a moment was transmitted through the spring to the valve member causing the Teflon seal in the valve member to turn on the seat in the valve body. This destroyed the pressure-tight seal formed between the Teflon and the valve seat and caused the valve to leak at pressures well below the desired leak pressure. It was then necesssary to permit the valve to set long enough to allow the Teflon to cold flow against the seat to re-form a new pressure-tight seal. This procedure in setting Teflon seated relief valves was time-consuming and frequently resulted in an undesirably wide deviation from the originally designed initial leak pressure.
The prior art also discloses that bearing means, and, more specifically, ball bearing means have long been utilized in valves. In one type of valve, the ball valve, the valve member is in effect a large ball bearing which easily turns upon its valve seats. Fluid flow through the valve is accomplished by a hole positioned through the middle of the large ball bearing.
Ball bearings have been utilized in conventional globe valves in order to more evenly distribute the load from the stem through the ball to the seat disc. Such a globe valve is shown and described in U.S. Pat. No. 2,848,187, issued Aug. 19, 1958 to the assignee of the present application. While the ball bearing in the U.S. Pat. No. 3,848,187 patent prevents the rotation of the valve member once it is seated, rotation of the valve member once it is lifted off the seat is inherent in the disclosure.